The present invention relates to an optical deflection device that deflects light by means of a rotation of a polygon mirror and to an image forming apparatus equipped with the optical deflection device, and in particular, to an optical deflection device and an image forming apparatus in both of which the number of parts are reduced to make a substantial cost reduction possible.
In a conventional optical deflection device used as an optical scanning means in a writing unit of an image forming apparatus such as a laser printer, a laser copying machine, a laser facsimile machine and a combined machine including the foregoing, a polygon mirror is rotated at high speed, and a beam emitted from a light source composed of a semiconductor laser is deflected by the rotating polygon mirror so that an image recording medium such as a photoreceptor drum is scanned by the beam.
An example of the conventional optical deflection device stated above is shown in FIG. 8. In this conventional optical deflection device, polygon mirror 200 is interposed between flange section 101 of body of rotation 100 and rotary yoke 102 to be incorporated solidly, and the body of rotation 100 in which the polygon mirror is incorporated is mounted rotatably on shaft portion 301 that is protruded on base 300 through bearing 400, while, magnet 103 is arranged on the rotary yoke 102 to face coil 303 attached on base board 302 that is provided on the base 300, thus, an electric current is made to flow through the coil 303 on the base 300 to rotate the body of rotation 100 through magnet 103 and thereby to rotate the polygon mirror 200 incorporated solidly in the body of rotation 100.
In the conventional optical deflection device as in the foregoing, there are many parts used because the body of rotation 100 is fixed on the bearing 400 mounted on the shaft portion 301 of the base 300, the polygon mirror 200 is incorporated in the flange section 101 of the body of rotation 100, and the magnet 103 is arranged on the rotary yoke 102 that is provided to interpose the polygon mirror 200 between itself and the flange section 101. Therefore, man-hour requirement for incorporating the polygon mirror 200 is great, resulting in a rise of manufacturing cost and a problem that an optical deflection device is made to be large.
With the background mentioned above, an object of the invention is to provide an optical deflection device wherein the number of parts needed to incorporate a polygon mirror is reduced sharply to achieve low cost and a small size of the optical deflection device and an image forming apparatus employing the optical deflection device.
Structure (1) to solve the problem stated above is represented by an optical deflection device having therein a body of rotation that is fixed on a bearing and is structured rotatably by a magnet arranged to face a coil provided on the base side, wherein the body of rotation is made of a magnet and a polygon mirror is fixed on the body of rotation.
Structure (2) is represented by the optical deflection device described in the Structure (1), wherein the body of rotation is made of a molded plastic magnet, and is fixed on the bearing through injection molding.
Structure (3) is represented by the optical deflection device described in the Structure (1), wherein the body of rotation is fixed on the bearing by means of either one of force fitting, shrinkage fitting and adhesion.
Structure (4) is represented by the optical deflection device described in the Structure (3), wherein the body of rotation is provided, on its portion that is in contact with the bearing, with a cut-out or irregularity.
Structure (5) is represented by the optical deflection device described in either one of the Structures (1), (2), (3) or (4), wherein the bearing is a dynamic pressure bearing.
Structure (6) is represented by the optical deflection device described in the Structures (5), wherein the dynamic pressure bearing is made of ceramic.
Structure (7) is represented by an image forming apparatus wherein light emitted from a light source is deflected by the optical deflection device described in either one of the Structures (1)-(6) to scan an image recording medium for recording images and thereby for forming images.